Absolute neutrino mass determination with the experiment KATRIN F. Glück (on behalf of the KATRIN collaboration) Johannes Gutenberg-Universität, Mainz email: fglueck@uni-mainz.de

Neutrino mass value important for: particle physics, astrophysics, cosmology Information for neutrino mass: neutrino oscillation experiments direct kinematical measurements neutrinoless double beta decay supernovae cosmological observations (galaxy redshift, microwave background radiation)

Neutrino oscillation results: At least 2 neutrino masses are finite; lepton mixing matrix has large off-diagonal elements SNO, KAMLAND: D m122 ≈7·10-5 eV2, θ12 ≈33° 3. SuperKamiokande: D m232 ≈ 2.5·10-3 eV2, θ23 ≈45° → mν(max) ≈ 50 meV m1 => m2 , m3 No information about absolute mass scale (m1) !

neutrino masses and schemes „normal“ mass hierarchy m1<m2<m3 quasi-degenerate hierarchical

Neutrino Mass Measurements Strategies cosmology & structure formation astrophysics: SN ToF measurements 0nbb decay: b decay kinematics: microcalorimeters MAC-E spectrometers NEMO3 76Ge @ LNGS ´90-´03 (71.7 kg×y) 2nbb D.N. Spergel et al: Smn < 0.69 eV (95%CL) S.W. Allen et al: Smn = 0.56 eV (best fit) |mee|=0.44+0.13-0.2 eV 187Re 3H SuperK, SNO, OMNIS + grav.waves: potential for ~1eV sensitivity?

Neutrino mass limit from cosmology: free-streaming of neutrinos in universe (because of their small interaction) massive neutrinos: gravitational effect, they can reduce the matter density fluctuations large neutrino mass → no small scale structure in universe neutrino mass limit from cosmology is model dependent (correlations with many other parameters)

mn = 0 eV mn = 1 eV Ma ’96 mn = 7 eV mn = 4 eV

2dFGRS analysis & n-mass limit 160.000 redshifts for 32 point galaxy power spectrum c2 = 32.9 large scales small scales ~900 Mpc ~90 Mpc

Cosmology: n-masses from WMAP & 2dFGRS & Ly a CMBR WMAP 220.000 galaxies with <z>=0.11 Powerspectrum of CMBR Combined result : mn < 0.23 eV (95 % CL.) astro-ph/0302209 a challenge for KATRIN ?! How are these results derived, and are they realistic?

2dFGRS analysis & n-mass limit adding priors for cosmological parameters Inference of neutrino mass depends on priors for Hubble parameter h, baryon density Wb h2, Wtot, flat prior on 0.1 < Wm < 0.5

WMAP results- a critical review 3 main lines of criticism: - Systematic problems of the WMAP result itself at large and small scales, compatibility with BBN, the role of the LCDM model (PL-LCDM or RSI-LCDM) - The role of priors and combination of different data sets (Hannestad, Elgaroy & Lahav) - ‚Massive attack‘ on LCDM: the role of H0 and the need for L and their influence on Wn (Rowan-Robinson & Sarkar)

need lab experiments with sub-eV mass sensitivity

Heidelberg Moscow (enriched 76Ge) Double  decay Z  E normal (2) neutrinoless (0) _ needed: a)  ν (Majorana) b) helicity flip: m()  0 or other new physics Heidelberg Moscow (enriched 76Ge)

Evidence for 0 at Heidelberg Moscow Exp.? Klapdor-Kleingrothaus et al., MPLA 37 (2001) 2409 (s.also comments: hep-ex/0202018, hep-ph/0205228, hep-ph/0205293) Nearly same data as earlier (54kgy: 8/1990 - 5/2000), but now asumptions of peaks in [2000,2080] keV:  background level is lower fit only [2032,2046] keV with background and peak  peak at 0 signal position (2039 keV) single side events expected peak position „Single-Side-Events“ erwartete Position T1/20 = (0.8 -18.3) 1025 y mee = (0.11 - 0.56) eV m(e) = (0.05 - 3.4) eV  (fast) degenerierte? New, data up to 2003: 72 kgy, with new data selection, new calibration Klapdor-Kleingrothaus et al., PL B586 (2004) 198  Peak at 2038.1(5) keV (expected: 2039.006(50) keV) Multi-Gauss. Fit: 4.2 significance for 0 T1/20 = (0.34-20.3) 1025 y mee = 0.1-0.9 eV (99.7% C.L.)

τ0ν-1 ~ mee2 · M0ν2 (1) mee = Σi Uei2 miν (2) If 0νββ due to light Majorana neutrino: τ0ν-1 ~ mee2 · M0ν2 (1) mee = Σi Uei2 miν (2) τ0ν → miν model dependent, because of: -nuclear matrix element sign (complex phase) of Uei2 possibility for beyond Standard Model mechanism of 0νββ process (supersymmetry, …) → Eq. 1 not valid any more Possible: present HM signal confirmed, but hierarchical neutrino masses ( miν < 0.2 eV) Test by KATRIN !

b – decay kinematics phase space determines energy spectrum transition energy E0 = Ee + En (+ recoil corrections) dN/dE = K × F(E,Z) × p × Etot × (E0-Ee) × [ (E0-Ee)2 – mn2 ]1/2 theoretical b spectrum near endpoint experimental observable 1 0.8 0.6 0.4 0.2 rel. rate [a.u.] strong source (high count rate near E0) small endpoint energy E0 excellent energy resolution long term stability low bg rate mn = 0eV mn = 1eV -3 -2 -1 0 Ee-E0 [eV]

m calorimeters for 187Re b decay neutrino mass measurement with array of 10 AgReO4 crystals lower pile up higher statistics MIBETA experiment (Milano, Como, Trento) M.Sisti et al, NIM A520(2004)125 A.Nucciotti et al, NIM A520(2004)148 C. Arnaboldi et al, PRL 91, 16802 (2003) E0 = 2.46 keV Top ~ 70-100mK

m calorimeters for 187Re b decay Kurie plot of 6.2 ×106 187Re b decay events above 700 eV fit with function free fit parameters: b endpoint energy mn2 b spectrum normal. pile-up amplitude background level

187Re b decay endpoint and mn E0 = 2465.3 ± 0.5stat ± 1.6syst eV (8751 h*mg, NIMA520, 2004) = 2466.1 ± 0.8stat ± 1.5syst eV (4485 h*mg, PRL91,2003) Flavio Gatti (Genoa): 0.5g Re  1—1.7eV sensitivity expected Expt. Under construction mn2 = -112 ± 207 ± 90 eV2 mn < 15 eV (90%CL) future: proposal for a new calorimeter expt. with ~2-3 eV sensitivity foreseen 2007 (?) fit range: 0.9 to 4 keV fit function

Direct determination of mν by tritium β decay super allowed E0 = 18.6 keV t1/2 = 12.3 a tritium  decay: 3H  3He+ +e-+e _ average neutrino mass Need: very high energy resolution & very high luminosity &  MAC-E-Filter very low background }

magnetic spectrometers & MAC-E filters

Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345) Two supercond. solenoids compose magnetic guiding field Electron source (T2) in left solenoid e- in forward direction: magnetically guided adiabatic transformation:  = E/B = const.  parallel e-beam Energy analysis by electrostat. retarding field E = EBmin/Bmax = EAs,eff/Aanalyse  4.8 eV (Mainz)

principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E) adiabatic magnetic guiding of b´s along field lines in stray B-field of s.c. solenoids: Bmax = 6 T Bmin = 3×10-4 T energy analysis by static retarding E-field with varying strength: high pass filter with integral b transmission for E>qU

The Mainz Neutrino Mass Experiment 1997-2001 Mainzer -Gruppe 2001: tilded solenoids new cryostat J. Bonn B. Bornschein* L. Bornschein* B. Flatt Ch. Kraus B. Müller** E.W. Otten J.P.Schall Th. Thümmler** Ch. Weinheimer** * FZ Karlsruhe **  Univ. Bonn T2 film at 1.86 K quench-condensed on graphite (HOPG) 45 nm thick (130ML), area 2cm2 thickness determination by ellipsometry

From current to future experiments Mainz: Troitsk: mn2 = -1.2(-0.7) ± 2.2 ± 2.1 eV2 mn2 = -2.3 ± 2.5 ± 2.0 eV2 mn < 2.2(2.3) eV (95%CL) mn < 2.1 eV (95%CL) C. Weinheimer, Nucl. Phys. B (Proc. Suppl.) 118 (2003) 279 V. Lobashev, private communication C. Kraus, EPS HEP2003 (neighbour excitations self-consistent) (allowing for a step function near endpoint) aim: improvement of mn by one order of magnitude (2eV  0.2eV )  improvement of uncertainty on mn2 by 100 (4eV2  0.04eV2) statistics: stronger Tritium source (>>1010 b´s/sec) longer measurement (~100 days  ~1000 days) energy resolution: DE/E=Bmin/Bmax  spectrometer with DE=1eV  Ø 10m UHV vessel

The KArlsruhe TRItium Neutrino Experiment Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft

Pre and main spectrometer transport magnets spectrometer solenoids Main spectrometer Energy resolution: E = 0.93 eV high luminosity: L = ASeff /4 = Aanalyse E/(2E) = 20 cm2 Ultrahigh vacuum requirements (Background) p < 10-11 mbar „simple“ construction: vacuum vessel at HV = electrode + „massless“ screening electrode industry study Pre spectrometer: Transmission of electron with highest energy only (10-7 part in last 100 eV)  Reduction of scattering probaility in main spectrometer  Reduction of background only moderate energy resolution required: E = 50 eV Test of new ideas (XHV, shape of electrodes, avoid and remove of trapped particles, ...) 1010 e-/s 103 e-/s

KATRIN Main Spectrometer stainless steel vessel (Ø=10m & l=22m) on HV potential minimisation of bg  UHV: p ≤ 10-11 mbar  „massless“ inner electrode system Mainz V results 2.8mHz inner electrode installed in Mainz spectrometer for background tests UHV requirements: outgassing < 10-13 mbar l/s inner surface ~ 800m2 volume to pump ~ 1500m3 intrinsic det. bg 1.6mHz

Detector

WGTS source characteristics pinj = 3.0 × 10-3 mbar ( at T=27K) qinj = 1.85 mbar l/s = 1020 mol./s = 4.7 Ci/s (~ 40g T2 per day if no closed loop) isotopic purity (±2‰) monitored by Laser Raman spectroscopy

Statistical uncertainty design optimisation ´01 -´03 tritium purity by tritium laboratory (>95%) 2× stronger gaseous source (Ø=75mm  Ø=90mm) requires Ø=10m spectrometer) optimised measuring point distribution (~5 eV below E0) active background reduction by inner electrode system, low background detector (needs further detailed tests) LoI reference

KATRIN sensitivity & discovery potential expectation: after 3 full beam years ssyst ~ sstat mn = 0.35eV (5s) mn = 0.3eV (3s) 5s discovery potential mn < 0.2eV (90%CL) sensitivity

Systematic uncertainties any not accounted variance s2 leads to negative shift of mn2: D mn2 = -2 s2 1. inelastic scatterings of ß´s inside WGTS - requires dedicated e-gun measurements, unfolding techniques for response fct. 2. fluctuations of WGTS column density (required < 0.1%) - rear detector, Laser-Raman spectroscopy, T=30K stabilisation, e-gun measurements 3. HV stability of retarding potential on ~3ppm level required - precision HV divider (PTB), monitor spectrometer beamline 4. WGTS charging due to remaining ions (MC:  < 20mV) - inject low energy meV electrons from rear side, diagnostic tools available 5. final state distribution - reliable quantum chem. calculations } a few contributions with each: m2 0.007 eV2

Status and schedule of Katrin 2001 Presentation of project to community (Bad Liebenzell Workshop) Foundation of KATRIN collaboration Letter of Intent (hep-ex/0109033) First, but significant funds by BMBF, FZ Karlsruhe 2002 Very positive report of International Review Panel 2003 X-Vat Workshop in Bad Liebenzell Background investigations at Mainz Setup of pre spectrometer at FZK 2004 Reviewing, proposal and funding 2004 - 2008 Setup of major KATRIN components: WGTS, transport system, main spectrometer, detector 2008 Commissioning at start of data taking with complete setup

Status of hardware components

Setup of pre-spectrometer at FZ Karlsruhe

Electric screening by „massless“ wire electrode   Secondary electrons from wall/electrode by cosmic rays, environmental radioactivity, ... wire electrode on slightly more negative potential U-U U test installation at Mainz

Electric screening by „massless“ wire electrode First realisation: Mainz III total background rate: 2.8mHz detector background rate 1.6mHz New record ! April 04 Mainz V (2004- PhD thesis: B. Flatt/Mz KATRIN pre spectrometer

Summary KATRIN: A large tritium  decay neutrino mass experiment at FZ Karlsruhe performed by a strong international collaboration with sub-eV sensitivity (<0.20 eV) probes in a unique model independent way: degenerate and cosmologically relevant neutrino masses complementary to oscillation experiments, 0nbb, cosmology  key experiment w.r.t. neutrino mass scale